An example of a printing apparatus is a digital offset printing apparatus, such as the Hewlett Packard (HP) Indigo line of digital printing presses which are based on digital offset color technology. These presses combine ink-on-paper quality with multi-color printing on a wide range of paper, foil and plastic substrates, i.e. print media. These digital printing presses offer cost-effective short-run printing, on-demand service, and on-the-fly color switching.
A digital offset printing apparatus works by using digitally controlled lasers or LED imaging modules for example, to create a latent image in the charged surface of a photo-imaging cylinder. The lasers are controlled according to digital instructions from a digital image file. Digital instructions typically include one or more of the following parameters: image color, image spacing, image intensity, order of the color layers, etc. Ink is then applied to the partially-charged surface of the photo-imaging cylinder, recreating the desired image (or a single color separation of a color image). The image is then transferred from the photo-imaging cylinder to a heated blanket cylinder, and from the blanket cylinder to the desired substrate, which is placed into contact with the blanket cylinder by means of an impression cylinder.
It is known in printing apparatus, for example digital offset printers, to use at least one binary ink developer (BID) to electrostatically transfer ink to the photo-imaging cylinder. A BID may include a developer roller in contact with the photo-imaging cylinder, allowing ink to be electrostatically transferred from the BID to the cylinder.
In known printers, the liquidity of an ink for transfer to a photo-imaging cylinder can reduce a quality of image printed using the ink. Known printers may use a squeegee roller in contact with a developer roller to reduce the liquidity of the ink, however the effectiveness of this method is limited.